INSTRUMENT OF AMENDMENT TO THE MDU RESOURCES GROUP, INC. 401(k) RETIREMENT PLAN

The MDU Resources Group, Inc. 401(k) Retirement Plan (as amended and restated March 1, 2011) (the “K-Plan”), is hereby further amended, as follows:

^1/Eligible employees participating in a management incentive compensation plan or an executive incentive compensation plan are not eligible for a Profit Sharing Contribution. Employees of the WBI Energy Corrosion Services division of WBI Energy Midstream, LLC are excluded from this feature.

^2/In the event a Participating Affiliate adopts a Profit Sharing Feature on a date other than January 1, effective as of the date of participation in the Plan, the amount of any such contribution allocated to a Supplement D‑1 Participant shall be based upon Compensation, received while in the employ of the Participating Affiliate after the date of acquisition by the Company or any Affiliate.

^3/Requirement to be an Active Employee on the last day of the Plan Year does not apply.

^4/The following participants of Kent’s Oil Service are granted vesting service for prior years of service with Spirit Road Oils: Isaias Jaimes, Hideo Lewis, Christopher Niffenegger, Jose Padilla, George Velador, and Anthony Willis.

^5/Eligible JTL Casper hourly employees (both union and nonunion), including those employees who participate in the Operating Engineers Local No. 800 & The Wyoming Contractors’ Association, Inc. Pension Trust Fund for Wyoming (JTL MEP employees.)

^1/Eligible employees participating in a management incentive compensation plan or an executive incentive compensation plan are not eligible for a Profit Sharing Contribution. Employees of the WBI Energy Corrosion Services division of WBI Energy Midstream, LLC are excluded from this feature.

^2/In the event a Participating Affiliate adopts a Profit Sharing Feature on a date other than January 1, effective as of the date of participation in the Plan, the amount of any such contribution allocated to a

Supplement D‑1 Participant shall be based upon Compensation, received while in the employ of the Participating Affiliate after the date of acquisition by the Company or any Affiliate.

^3/Requirement to be an Active Employee on the last day of the Plan Year does not apply.

^4/The following participants of Kent’s Oil Service are granted vesting service for prior years of service with Spirit Road Oils: Isaias Jaimes, Hideo Lewis, Christopher Niffenegger, Jose Padilla, George Velador, and Anthony Willis.

^5/Eligible JTL Casper hourly employees (both union and nonunion), including those employees who participate in the Operating Engineers Local No. 800 & The Wyoming Contractors’ Association, Inc. Pension Trust Fund for Wyoming (JTL MEP employees.)

^6/Eligible salaried employees of JTL hired after December 31, 2014 or any other JTL employee who transfers to a salaried position after December 31, 2014.

For each Plan Year, JTL shall provide eligible hourly Participants $1.55 (effective April 1, 2014) per hour of service as a Retirement Contribution. The amount of any such contribution for a Plan Year will be allocated to Supplement D-7 hourly Participants for each hour of service for which the Participant receives compensation, excluding Hours of Service pursuant to a prevailing wage agreement. In addition, JTL will credit eligible salaried Participants with a contribution equal to eight percent (8%) of Compensation. Salaried Participants must have been hired and classified as a salaried employee prior to January 1, 2015 in order to receive a Retirement Contribution allocation. The amount of any such Retirement Contribution for a Plan Year shall be allocated to Supplement D‑7 Participants based upon their Compensation, excluding bonuses received while employed by the identified Participating Affiliate.

IN WITNESS WHEREOF, MDU Resources Group, Inc., as Sponsoring Employer of the Plan, has caused this amendment to be duly executed by a member of the MDU Resources Group, Inc. Employee Benefits Committee (“Committee”) on this 11th day of

December, 2014.